After screening visit patients were booked for arthroscopy and at that time they were randomised to either ACT3D-CS with co.don chondrosphere® (Group A) or to MF(Group B), a marrow-stimulating method based on the penetration of the subchondral bone plate at the bottom of the cartilage defect. At the time of arthroscopy Patients of group B had their procedure of MF (treatment surgery) and patients of group A had their cells harvested from healthy cartilage. The cells are cultivated for 8-10 weeks in vitro to develope 3-dimensional spheroids , that are transplanted in an open knee procedure (treatment surgery)into the defect. Patients subsequently followed the same rehabilitation program and had post-surgery visits. After the 12-month-visit a interim analyses will be performed and the 24-month-visit is defined as final assessment. Then patients have follow-up assessments up to 60 months post-treatment-surgery.